Dymamic Response And Mechanical Coupling Behavior Of Deep Water Riser System

Deep water resources drilling is one of the most advanced technologies home and abroad.The deepwater drilling platform is always in the severe and complicated ocean environment.The research object in this article is a component which is closely related to offshore drilling—deepwater riser. Deepwater riser is an important component that connects offshore drillingplatform and subsea wellhead. Risers are also susceptible to sea current. With increasing lengthof riser and operation depth subsea, the stress state of riser is more and more complicated.Therefore, research on mechanical analysis of deepwater riser system is a vital topic. The mainresearch progresses are listed as follows:(1) Deep water drilling riser transverse vibratory response analysisFirst, environmental loads such as sea wind, sea tide, current, wave force which influenceriser transverse vibration are calculated and analyzed. After that, according to the character ofdeformation of great deformation by small strain, deep water riser transverse vibrationdifferential equation considering offshore platform and internal operation drill strings byd’Alembert principle is established, and the deformation of deep water riser sample analysis canbe achieved by finite difference numerical method.(2) Deep water drilling riser vibration sensitivity factors analysisThe deep water riser dynamic response influencing factors are a lot, such as top tension ofriser, ocean wave force, sea current motion parameters, influence of the platform motion, riserstructure. In this article, change of riser top tension, settle of riser buoyancy module, period ofwave motion and drift of drilling platform sensitivity factors are analyzed, and the result canprovide theoretical basis of riser design.(3) Deep water riser vortex–induced vibration effect analysis considering effect ofauxiliary pipeline evaluation and analysis.Deep water riser vortex–induced vibration effect has been numerical modeled by largescaled software—Fluent.In this paper, there are two parameters, which affect the vortex-induced result: lift coefficient whose flow direction perpendicular to ocean current and vortex-induced drag coefficient, which flows downstream. Evaluation of the riser vortex-induced resultis based on these two parameters.First, riser vortex–induced vibration response under singlecylinder circular flow condition is simulated, and the result is in agreement with classicexperiment result, therefore, accuracy of simulated condition can be validated; After that, howthe auxiliary pipeline affects the vortex–induced vibration of the riser is focused on.Quantitative description of pull off after the vortex with effect of auxiliary pipeline can be givenby analysis of lift coefficient and drag coefficient and data processing of simulation result withspectral response analysis.(4) Coupled analysis between deep water riser and top tension systemMany factors affects deep water riser dynamic response such as drilling ship heave, roll,pitch. Meanwhile, the top tension system causes transverse excitations in two directions, which include in plane and out of plane. In this paper, coupling model is established between riser andtop tension system, which considering the float motion response in ocean currents, and itprovides a method to analysze riser dynamic response under the condition of the top tensionsystem.(5) Coupled analysis between deep water riser and internal drillstringAnother important factor is the influence of drill string in the riser dynamic response.Typically, internal drill string in the riser has two kinds of motion state, namely autorotation ofthe drillstring and revolution in the riser, and it also accompanied by the drill string vibration.According to the principle of force, coupling model is established between riser and drill string,it also gives the solution model, and the effect of drill string has been analyzed.(6) Fatigue life analysis of deep water riser under the condition of the stress ratioIt is very important to use safely deep water riser which endure alternating stress load inthe complex ocean environment. Therefore, it is necessary to accurately predict stress andfatigue life of deep water riser. In this paper, based on the theory of fracture mechanics, themodel which considering structural crack is used to analyze fatigue life of deep riser under thecondition of alternating stress, which provides a new theoretical analysis method to predict thefatigue life of riser.